"This won't take more than three or four weeks. From that moment onwards, we acquire rights and we acquire obligations."

The obligations are that Esa carries out flights of its new logistics spacecraft, the Automated Transfer Vehicle (ATV), to the ISS roughly once every 12 months.

As rights, Esa gets a percentage of space station crew time and also flight opportunities.

European astronauts currently get one six-month flight every two years, but Esa is negotiating to acquire flights currently allocated to the Italian Space Agency (Asi), which would give it access to the ISS once a year.

The orbital lab is equipped with 10 experiment racks, each about the size of a telephone booth. Eight of these are situated in the side walls and two in the ceiling.

In addition, Columbus will carry two experiment payloads on the outside of its pressurised hull.

Payloads are partly geared towards investigating the problems humans would face on missions to Mars.

But, explains Thomas Reiter, a European astronaut and executive at the German Aerospace Center (DLR): "The majority of scientific research that will be done on Columbus is dedicated to fields that are of interest to our life here on Earth.

"There are many human diseases which are not yet fully understood, and research in microgravity could make a contribution in understanding the roots of some diseases rather than just the symptoms."

One such investigation planned for Columbus will examine the effects of weightlessness on the immune system, which plays important roles in numerous diseases, including cancers and Aids.

Certain effects of the immune system are activated or deactivated in different gravity environments. Understanding how weightlessness affects the immune system might help researchers to develop new strategies for tackling disease.

Addressing fundamentals

Other experiments could help advance understanding of osteoporosis, lead to improvements in the aluminium casting process - which is crucial in the motor industry - and result in food crops that are more resistant to disease and drought.

European Physiology Modules Facility (EPM) - a set of experiments to investigate the effects of long-duration spaceflight on the human body

Fluid Science Laboratory (FSL) - will be used to study how fluids behave in microgravity

European Drawer Rack (EDR) - a carrier system designed to house experimental modules in drawers and lockers

European Transport Carrier (ETC) - will serve as a workbench and stowage facility

However, some researchers are less than enthusiastic about the scientific value of investigations carried out on Columbus.

"The Columbus laboratory certainly doesn't address any fundamental questions in science - in astronomy or fundamental physics, for instance," says Nobel laureate Steven Weinberg, a theoretical physicist from the University of Texas, Austin.

"It is really an exercise in technology. [And] I think a lot of the work is aimed at improving our knowledge of microgravity, which doesn't seem to me very important unless you're going to be spending a lot of time in space for some other reason.

"Since I think manned spaceflight is not a cost-effective way of doing science, I'm not impressed by that sort of research."

Professor Weinberg said an experiment originally designated for the space station called the Alpha Magnetic Spectrometer (AMS), which carries a price tag above $1bn, might now be mothballed due to limited space on the few remaining shuttle flights before Nasa retires the orbiter in 2010.

Many in the physics community regarded this cosmic ray detection experiment as capable of providing important new insights into the Universe.

SOLAR - a platform with three scientific instruments to study Sun-related phenomena

The Columbus project was hit by several hold-ups in space station construction which allowed its costs to rise.

The first of these occurred between 1996 and 2000 and was due to Russian delays in launching the space station's main control and habitation module, Zvezda.

Further delay resulted from the destruction of space shuttle Columbia in 2003, which claimed the lives of seven astronauts. The US space agency spent two years and more than $1bn fixing the shuttle for a return to flight in 2005.

However, the shuttle fleet was swiftly grounded again for a further year after the same problem responsible for dooming Columbia - foam shedding from the external fuel tank - re-emerged on the 2005 mission.

According to Alan Thirkettle, a cost overrun of just 4% in these circumstances was acceptable and displayed good management of the project.

Michael Menking, senior vice-president at EADS Astrium, the prime contractor on Columbus, said the delays had an upside.

"They gave us the opportunity to prepare for installing an additional communications terminal inside Columbus at some point in the future. We were also able to carry out extra tests on the internal and external payloads," he told BBC News.

Esa will use a dedicated centre in southern Germany to control activities on Columbus.